Security Experts:

Severe DoS Flaw Discovered in Siemens SIMATIC PLCs

Siemens informed customers on Tuesday that some of its SIMATIC S7-400 CPUs are affected by a high severity denial-of-service (DoS) vulnerability.

SIMATIC S7-400 is a family of programmable logic controllers (PLCs) designed for process control in industrial environments. The product is used worldwide in the automotive, mechanical equipment manufacturing, building engineering, steel, power generation and distribution, chemical, warehousing, food, and pharmaceutical sectors.

Siemens discovered that these devices fail to properly validate S7 communication packets, allowing a remote attacker to trigger a DoS condition that causes the system to enter DEFECT mode and remain so until it’s manually restarted.Vulnerability found in Siemens SIMATIC S7-400 PLCs

“Successful exploitation requires an attacker to be able to send a specially crafted S7 communication packet to a communication interface of the CPU. This includes Ethernet, PROFIBUS, and Multi Point Interfaces (MPI),” Siemens said in its advisory. “No user interaction or privileges are required to exploit the security vulnerability. The vulnerability could allow causing a Denial-of-Service condition of the core functionality of the CPU, compromising the availability of the system.”

The German industrial giant says it’s not aware of any instances where this vulnerability has been exploited for malicious purposes.

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The security hole, tracked as CVE-2018-4850 with a CVSS score of 7.5, impacts S7-400 CPUs with hardware version 4.0 and earlier, S7-400 CPUs with hardware version 5.0 prior to 5.2, and S7-400H CPUs with hardware version 4.5 and earlier. In order to patch the vulnerability, users have been advised to update to hardware versions 5.0, 5.2 and 6.0, respectively.

Siemens pointed out that the affected hardware versions are either in the process of being cancelled or have already been phased out.

Organizations should apply the updates as soon as possible considering that DoS vulnerabilities can pose a serious risk in industrial environments.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.